Passive reactor containment protection system

ABSTRACT

A nuclear reactor containment system with passive cooling capabilities. In one embodiment, the system includes an inner containment vessel for housing a nuclear steam supply system and an outer containment enclosure structure. An annular water-filled reservoir may be provided between the containment vessel and containment enclosure structure which provides a heat sink for dissipating thermal energy, in the event of a thermal energy release incident inside the containment vessel, the reactor containment system provides passive water and air cooling systems operable to regulate the heat of the containment vessel and the equipment inside. In one embodiment, cooling water makeup to the system is not required to maintain containment vessel and reactor temperatures within acceptable margins.

CROSS-REFERENCE TO RELATED PATENT APPLICATIONS

The present application is a U.S. national stage application under 35U.S.C. 371 of PCI Application No. PCT/US2013/042070 filed May 21, 2013,which claims the benefit of U.S. Provisional Patent Application Ser. No.61/649,593 filed May 21, 2012, the entireties of which are incorporatedherein by reference.

FIELD OF THE INVENTION

The present invention relates nuclear reactors, and more particularly toa reactor containment system with passive thermal energy releasecontrol.

BACKGROUND OF THE INVENTION

The containment for a nuclear reactor is defined as the enclosure thatprovides environmental isolation to the nuclear steam supply system(NSSS) of the plant in which nuclear fission is harnessed to producepressurized steam. A commercial nuclear reactor is required to beenclosed in a pressure retaining structure which can withstand thetemperature and pressure resulting from the most severe accident thatcan be postulated for the facility. The most severe energy releaseaccidents that can be postulated for a reactor and its containment canbe of two types.

First, an event that follows a loss-of-coolant accident (LOCA) andinvolve a rapid large release of thermal energy from the plant's nuclearsteam supply system (NSSS) due to a sudden release of reactor's coolantin the containment space. The reactor coolant, suddenly depressurized,would violently flash resulting in a rapid rise of pressure andtemperature in the containment space. The in-containment space isrendered into a mixture of air and steam. LOCA can be crediblypostulated by assuming a sudden failure in a pipe carrying the reactorcoolant.

Another second thermal event of potential risk to the integrity of thecontainment is the scenario wherein all heat rejection paths from theplant's nuclear steam supply system (NSSS) are lost, forcing the reactorinto a “scram.” A station black-out is such an event. The decay heatgenerated in the reactor must be removed to protect it from anuncontrolled pressure rise.

More recently, the containment structure has also been called upon bythe regulators to withstand the impact from a crashing aircraft.Containment structures have typically been built as massive reinforcedconcrete domes to withstand the internal pressure from LOCA. Althoughits thick concrete wall could be capable of withstanding an aircraftimpact, it is also a good insulator of heat, requiring pumped heatrejection systems (employ heat exchangers and pumps) to reject itsunwanted heat to the external environment (to minimize the pressure riseor to remove decay heat). Such heat rejection systems, however, rely ona robust power source (off-site or local diesel generator, for example)to power the pumps. The station black out at Fukushima in the wake ofthe tsunami is a sobering reminder of the folly of relying on pumps.

Present day containment structures with their monolithic reinforcedconcrete construction make it extremely difficult and expensive toremove and install a large capital requirement such as a steam generatorin the NSSS enclosed by them. To make a major equipment change out, ahatch opening in the thick concrete dome has to be made at great expenseand down time for the reactor. Unfortunately, far too many steamgenerators have had to be changed out at numerous reactors in the past25 years by cutting through the containment dome at billions of dollarsin cost to the nuclear power industry.

The above weaknesses in the state-of-the-art call for an improvednuclear reactor containment system.

SUMMARY OF THE INVENTION

The present invention provides nuclear reactor containment system thatovercomes the deficiencies of the foregoing arrangements. Thecontainment system generally includes an inner containment vessel whichmay be formed of steel or another ductile material and an outercontainment enclosure structure (CES) thereby forming a double walledcontainment system. In one embodiment, a water-filled annulus may beprovided between the containment vessel and the containment enclosurestructure providing an annular cooling reservoir. The containment vesselmay include a plurality of longitudinal heat transfer fins which extend(substantially) radial outwards from the vessel in the manner of “fin”.The containment vessel thus serves not only as the primary structuralcontainment for the reactor, but is configured and operable to functionas a heat exchanger with the annular water reservoir acting as the heatsink. Accordingly, as further described herein, the containment vesseladvantageously provides a passive (i.e. non-pumped) heat rejectionsystem when needed during a thermal energy release accident such as aLOCA or reactor scram to dissipate heat and cool the reactor.

In one embodiment according to the present disclosure, a nuclear reactorcontainment system includes a containment vessel configured for housinga nuclear reactor, a containment enclosure structure (CES) surroundingthe containment vessel, and an annular reservoir formed between thecontainment vessel and containment enclosure structure (CES) forextracting heat energy from the containment space. In the event of athermal energy release incident inside the containment vessel, heatgenerated by the containment vessel is transferred to the annularreservoir which operates to cool the containment vessel. In oneembodiment, the annular reservoir contains water for cooling thecontainment vessel. A portion of the containment vessel may includesubstantially radial heat transfer fins disposed in the annularreservoir and extending between the containment vessel and containmentenclosure structure (CES) to improve the dissipation of heat to thewater-filled annular reservoir. When a thermal energy release incidentoccurs inside the containment vessel, a portion of the water in theannulus is evaporated and vented to atmosphere through the containmentenclosure structure (CES) annular reservoir in the form of water vapor.

Embodiments of the system may further include an auxiliary air coolingsystem including a plurality of vertical inlet air conduits spacedcircumferentially around the containment vessel in the annularreservoir. The air conduits are in fluid communication with the annularreservoir and outside ambient air external to the containment enclosurestructure (CES). When a thermal energy release incident occurs insidethe containment vessel and water in the annular reservoir issubstantially depleted by evaporation, the air cooling system becomesoperable by providing a ventilation path from the reservoir space to theexternal ambient. The ventilation system can thus be viewed as asecondary system that can continue to cool the containment ad infinitum.

According to another embodiment, a nuclear reactor containment systemincludes a containment vessel configured for housing a nuclear reactor,a containment enclosure structure (CES) surrounding the containmentvessel, a water filled annulus formed between the containment vessel andcontainment enclosure structure (CES) for cooling the containmentvessel, and a plurality of substantially radial fins protruding outwardsfrom the containment vessel and located in the annulus. In the event ofa thermal energy release incident inside the containment vessel, heatgenerated by the containment vessel is transferred to the water filledreservoir in the annulus through direct contact with the externalsurface of the containment vessel and its fins substantially radial thuscooling the containment vessel. In one embodiment, when a thermal energyrelease incident occurs inside the containment vessel and water in theannulus is substantially depleted by evaporation, the air cooling systemis operable to draw outside ambient air into the annulus through the airconduits to cool the heat generated in the containment (which decreasesexponentially with time) by natural convection. The existence of waterin the annular region completely surrounding the containment vessel willmaintain a consistent temperature distribution in the containment vesselto prevent warping of the containment vessel during the thermal energyrelease incident or accident.

In another embodiment, a nuclear reactor containment system includes acontainment vessel including a cylindrical shell configured for housinga nuclear reactor, a containment enclosure structure (CES) surroundingthe containment vessel, an annular reservoir containing water formedbetween the shell of the containment vessel and containment enclosurestructure (CES) for cooling the containment vessel, a plurality ofexternal (substantially) radial fins protruding outwards from thecontainment vessel into the annulus, and an air cooling system includinga plurality of vertical inlet air conduits spaced circumferentiallyaround the containment vessel in the annular reservoir. The air conduitsare in fluid communication with the annular reservoir and outsideambient air external to the containment enclosure structure (CES). Inthe event of a thermal energy release incident inside the containmentvessel, heat generated by the containment vessel is transferred to theannular reservoir via the (substantially) radial containment wall alongwith its internal and external fins which operates to cool thecontainment vessel.

Advantages and aspects of a nuclear reactor containment system accordingto the present disclosure include the following:

Containment structures and systems configured so that a severe energyrelease event as described above can be contained passively (e.g.without relying on active components such as pumps, valves, heatexchangers and motors);

Containment structures and systems that continue to work autonomouslyfor an unlimited duration (e.g. no time limit for human intervention);

Containment structures fortified with internal and external ribs(fins)configured to withstand a projectile impact such as a crashingaircraft without losing its primary function (i.e. pressure &radionuclide (if any) retention and heat rejection); and

Containment vessel equipped with provisions that allow for the readyremoval (or installation) of major equipment through the containmentstructure.

BRIEF DESCRIPTION OF THE DRAWINGS

The features of the illustrative embodiments of the present inventionwill be described with reference to the following drawings, where likeelements are labeled similarly, and in which:

FIG. 1 is side elevation view of a tinned primary reactor containmentvessel according to the present disclosure which forms part of a nuclearreactor containment system, the lower portions of some fins being brokenaway in part to reveal vertical support columns and circumferential rib:

FIG. 2 is transverse cross-sectional view thereof taken along lineII-II;

FIG. 3 is a detail of item III in FIG. 2;

FIG. 4 is a longitudinal cross-sectional view of the nuclear reactorcontainment system showing the containment vessel of FIG. 1 and outercontainment enclosure structure (CES) with water filled annularreservoir formed between the vessel and enclosure:

FIG. 5 is a longitudinal cross-sectional view through the containmentvessel and containment enclosure structure (CES);

FIG. 6 is a side elevation view of nuclear reactor containment system asinstalled with the outer containment enclosure structure (CES) beingvisible above grade:

FIG. 7 is a top plan view thereof:

FIG. 8 is longitudinal cross-sectional view thereof taken along lineVIII-VIII in FIG. 7 showing both above and below grade portions of thenuclear reactor containment system;

FIG. 9 is side elevation view of the primary reactor containment vesselshowing various cross-section cuts to reveal equipment housed in andadditional details of the containment vessel;

FIG. 10 is a top plan view thereof;

FIG. 11 is a longitudinal cross-sectional view thereof taken along lineXI-XI in FIG. 10;

FIG. 12 is a longitudinal cross-sectional view thereof taken along lineXII-XII in FIG. 10;

FIG. 13 is a transverse cross-sectional view thereof taken along lineXIII-XIII in FIG. 9;

FIG. 14 is a transverse cross-sectional view thereof taken along lineXIV-XIV in FIG. 9;

FIG. 15 is a transverse cross-sectional view thereof taken along lineXV-XV in FIG. 9;

FIG. 16 is a partial longitudinal cross-sectional view of the nuclearreactor containment system showing an auxiliary heat dissipation system;

FIG. 17 is an isometric view of the containment vessel with lowerportions of the (substantially) radial fins of the containment vesselbroken away in part to reveal vertical support columns andcircumferential rib;

FIG. 18 is a longitudinal cross-sectional view of a portion of the heatdissipation system of FIG. 16 showing upper and lower ring headers andducts attached to the shell of the containment vessel; and

FIG. 19 is a schematic depiction of a generalized cross-section of thenuclear reactor containment system and operation of the water filledannular reservoir to dissipate heat and cool the containment vesselduring a thermal energy release event.

All drawings are schematic and not necessarily to scale.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The features and benefits of the invention are illustrated and describedherein by reference to illustrative embodiments. This description ofillustrative embodiments is intended to be read in connection with theaccompanying drawings, which are to be considered part of the entirewritten description. In the description of embodiments disclosed herein,any reference to direction or orientation is merely intended forconvenience of description and is not intended in any way to limit thescope of the present invention. Relative terms such as “lower,” “upper,”“horizontal,” “vertical,”, “above,” “below,” “up,” “down,” “top” and“bottom” as well as derivative thereof (e.g., “horizontally,”“downwardly,” “upwardly,” etc.) should be construed to refer to thenominal orientation as then described or as shown in the drawing underdiscussion. These relative terms are for convenience of description onlyand do not require that the apparatus be constructed or operated in arigorously specific orientation denoted by the term. Terms such as“attached,” “affixed.” “connected.” “coupled,” “interconnected,” andsimilar refer to a relationship wherein structures are secured orattached to one another either directly or indirectly throughintervening structures, as well as both movable or rigid attachments orrelationships, unless expressly described otherwise. Accordingly, thedisclosure expressly should not be limited to such illustrativeembodiments illustrating some possible non-limiting combination offeatures that may exist alone or in other combinations of features.

Referring to FIGS. 1-15, a nuclear reactor containment system 100according to the present disclosure is shown. The system 100 generallyincludes an inner containment structure such as containment vessel 200and an outer containment enclosure structure (CES) 300 collectivelydefining a containment vessel-enclosure assembly 200-300. Thecontainment vessel 200 and containment enclosure structure (CES) 300 arevertically elongated and oriented, and defines a vertical axis VA.

In one embodiment, the containment vessel-enclosure assembly 200-300 isconfigured to be buried in the subgrade at least partially below grade(see also FIGS. 6-8). The containment vessel-enclosure assembly 200-300may be supported by a concrete foundation 301 comprised of a bottom slab302 and vertically extending sidewalls 303 rising from the slab forminga top base mat 304. The sidewalls 303 may circumferentially enclosecontainment vessel 200 as shown wherein a lower portion of thecontainment vessel may be positioned inside the sidewalls. In someembodiments, the sidewalls 303 may be poured after placement of thecontainment vessel 200 on the bottom slab 302 (which may be poured andset first) thereby completely embedding the lower portion of thecontainment vessel 200 within the foundation. The foundation walls 303may terminate below grade in some embodiments as shown to provideadditional protection for the containment vessel-enclosure assembly200-300 from projectile impacts (e.g. crashing plane, etc.). Thefoundation 301 may have any suitable configuration in top plan view,including without limitation polygonal (e.g. rectangular, hexagon,circular, etc.).

In one embodiment, the weight of the containment vessel 200 may beprimarily supported by the bottom slab 302 on which the containmentvessel rests and the containment enclosure structure (CES) 300 may besupported by the base mat 304 formed atop the sidewalls 303 of thefoundation 301. Other suitable vessel and containment enclosurestructure (CES) support arrangements may be used.

With continuing reference to FIGS. 1-15, the containment structure 200may be an elongated vessel 202 including a hollow cylindrical shell 204with circular transverse cross-section defining an outer diameter D1, atop head 206, and a bottom head 208. In one embodiment, the containmentvessel 200 (i.e. shell and heads) may be made from a suitably strong andductile metallic plate and bar stock that is readily weldable (e.g. lowcarbon steel). In one embodiment, a low carbon steel shell 204 may havea thickness of at least 1 inch. Other suitable metallic materialsincluding various alloys may be used.

The top head 206 may be attached to the shell 204 via a flanged joint210 comprised of a first annular flange 212 disposed on the lower end orbottom of the top head and a second mating annular flange 214 disposedon the upper end or top of the shell. The flanged joint 210 may be abolted joint, which optionally may further be seal welded after assemblywith a circumferentially extending annular seal weld being made betweenthe adjoining flanges 212 and 214.

The top head 206 of containment vessel 200 may be an ASME (AmericanSociety of Mechanical Engineers) dome-shaped flanged and dished head toadd structural strength (i.e. internal pressure retention and externalimpact resistance), however, other possible configurations including aflat top head might be used. The bottom head 208 may similarly be adome-shaped dished head or alternatively flat in other possibleembodiments. In one containment vessel construction, the bottom head 208may be directly welded to the lower portion or end of the shell 204 viaan integral straight flange (SF) portion of the head matching thediameter of shell. In one embodiment, the bottom of the containmentvessel 200 may include a ribbed support stand 208 a or similar structureattached to the bottom head 208 to help stabilize and provide levelsupport for the containment vessel on the slab 302 of the foundation301, as further described herein.

In some embodiments, the top portion 216 of the containment vessel shell204 may be a diametrically enlarged segment of the shell that forms ahousing to support and accommodate a polar crane (not shown) for movingequipment, fuel, etc. inside the containment vessel. This will providecrane access to the very inside periphery of the containment vessel andenable placement of equipment very close to the periphery of thecontainment vessel 200 making the containment vessel structure compact.In one configuration, therefore, the above grade portion of thecontainment vessel 200 may resemble a mushroom-shaped structure.

In one possible embodiment, the enlarged top portion 216 of containmentvessel 200 may have an outer diameter D2 that is larger than the outerdiameter D1 of the rest of the adjoining lower portion 218 of thecontainment vessel shell 204. In one non-limiting example, the topportion 216 may have a diameter D2 that is approximately 10 feet largerthan the diameter D1 of the lower portion 218 of the shell 204. The topportion 216 of shell 204 may have a suitable height H2 selected toaccommodate the polar crane with allowance for working clearances whichmay be less than 50% of the total height H1 of the containment vessel200. In one non-limiting example, approximately the top ten feet of thecontainment vessel 200 (H2) may be formed by the enlarged diameter topportion 216 in comparison to a total height H1 of 200 feet of thecontainment vessel. The top portion 216 of containment vessel 200 mayterminate at the upper end with flange 214 at the flanged connection tothe top head 206 of the containment vessel.

In one embodiment, the diametrically enlarged top portion 216 ofcontainment vessel 200 has a diameter D2 which is smaller than theinside diameter D3 of the containment enclosure structure (CES) 300 toprovide a (substantially) radial gap or secondary annulus 330 (see, e.g.FIG. 4). This provides a cushion of space or buffer region between thecontainment enclosure structure (CES) 300 and containment vessel topportion 216 in the advent of a projectile impact on the containmentenclosure structure (CES). Furthermore, the annulus 330 furthersignificantly creates a flow path between primary annulus 313 (betweenthe shells of the containment enclosure structure (CES) 300 andcontainment vessel 200) and the head space 318 between the containmentenclosure structure (CES) dome 316 and top head 206 of the containmentvessel 200 for steam and/or air to be vented from the containmentenclosure structure (CES) as further described herein. Accordingly, thesecondary annulus 330 is in fluid communication with the primary annulus313 and the head space 318 which in turn is in fluid communication withvent 317 which penetrates the dome 316. In one embodiment, the secondaryannulus 330 has a smaller (substantially) radial width than the primaryannulus 313.

Referring to FIGS. 1-4, the containment enclosure structure (CES)structure (CES) 300 may be double-walled structure in some embodimentshaving sidewalls 320 formed by two (substantially) radially spaced andinterconnected concentric shells 310 (inner) and 311 (outer) with plainor reinforced concrete 312 installed in the annular space between them.The concentric shells 310, 311 may be made of any suitably strongmaterial, such as for example without limitation ductile metallic platesthat are readily weldable (e.g. low carbon steel). Other suitablemetallic materials including various alloys may be used. In oneembodiment, without limitation, the double-walled containment enclosurestructure (CES) 300 may have a concrete 312 thickness of 6 feet or morewhich ensures adequate ability to withstand high energy projectileimpacts such as that from an airliner.

The containment enclosure structure (CES) 300 circumscribes thecontainment vessel shell 204 and is spaced (substantially) radiallyapart from shell 204, thereby creating primary annulus 313. Annulus 313may be a water-filled in one embodiment to create a heat sink forreceiving and dissipating heat from the containment vessel 200 in thecase of a thermal energy release incident inside the containment vessel.This water-filled annular reservoir preferably extends circumferentiallyfor a full 360 degrees in one embodiment around the perimeter of upperportions of the containment vessel shell 204 lying above the concretefoundation 301. FIG. 4 shows a cross-section of the water-filled annulus313 without the external (substantially) radial fins 221 in this figurefor clarity. In one embodiment, the annulus 313 is filled with waterfrom the base mat 304 at the bottom end 314 to approximately the top end315 of the concentric shells 310, 311 of the containment enclosurestructure (CES) 300 to form an annular cooling water reservoir betweenthe containment vessel shell 204 and inner shell 310 of the containmentenclosure structure (CES). This annular reservoir may be coated or linedin some embodiments with a suitable corrosion resistant material such asaluminum, stainless steel, or a suitable preservative for corrosionprotection. In one representative example, without limitation, theannulus 313 may be about 10 feet wide and about 100 feet high.

In one embodiment, the containment enclosure structure (CES) 300includes a steel dome 316 that is suitably thick and reinforced toharden it against crashing aircraft and other incident projectiles. Thedome 316 may be removably fastened to the shells 310, 311 by a robustflanged joint 318. In one embodiment, the containment enclosurestructure (CES) 300 is entirely surrounded on all exposed above gradeportions by the containment enclosure structure (CES) 300, whichpreferably is sufficiently tall to provide protection for thecontainment vessel against aircraft hazard or comparable projectile topreserve the structural integrity of the water mass in the annulus 313surrounding the containment vessel. In one embodiment, as shown, thecontainment enclosure structure (CES) 300 extends vertically below gradeto a substantial portion of the distance to the top of the base mat 304.

The containment enclosure structure (CES) 300 may further include atleast one rain-protected vent 317 which is in fluid communication withthe head space 318 beneath the dome 316 and water-filled annulus 313 toallow water vapor to flow, escape, and vent to atmosphere. In oneembodiment, the vent 317 may be located at the center of the dome 316.In other embodiments, a plurality of vents may be provided spaced(substantially) radially around the dome 316. The vent 317 may be formedby a short section of piping in some embodiments which is covered by arain hood of any suitable configuration that allows steam to escape fromthe containment enclosure structure (CES) but minimizes the ingress ofwater.

In some possible embodiments, the head space 318 between the dome 316and top head 206 of the containment vessel 200 may be filled with anenergy absorbing material or structure to minimize the impact load onthe containment enclosure structure (CES) dome 316 from a crashing(falling) projecting (e.g. airliner, etc.). In one example, a pluralityof tightly-packed undulating or corrugated deformable aluminum platesmay be disposed in part or all of the head space to form a crumple zonewhich will help absorb and dissipate the impact forces on the dome 316.

Referring primarily to FIGS. 1-5 and 8-17, the buried portions of thecontainment vessel 200 within the concrete foundation 301 below the basemat 304 may have a plain shell 204 without external features. Portionsof the containment vessel shell 204 above the base mat 304, however, mayinclude a plurality of longitudinal external (substantially) radial ribsor fins 220 which extend axially (substantially) parallel to verticalaxis VA of the containment vessel-enclosure assembly 200-300. Theexternal longitudinal fins 220 are spaced circumferentially around theperimeter of the containment vessel shell 204 and extend (substantially)radially outwards from the containment vessel.

The ribs 220 serve multiple advantageous functions including withoutlimitation (1) to stiffen the containment vessel shell 204, (2) preventexcessive “sloshing” of water reserve in annulus 313 in the occurrenceof a seismic event, and (3) significantly to act as heat transfer “fins”to dissipate heat absorbed by conduction through the shell 204 to theenvironment of the annulus 313 in the situation of a fluid/steam releaseevent in the containment vessel.

Accordingly, in one embodiment to maximize the heat transfereffectiveness, the longitudinal fins 220 extend vertically forsubstantially the entire height of the water-filled annulus 313 coveringthe effective heat transfer surfaces of the containment vessel 200 (i.e.portions not buried in concrete foundation) to transfer heat from thecontainment vessel 200 to the water reservoir, as further describedherein. In one embodiment, the external longitudinal fins 220 have upperhorizontal ends 220 a which terminate at or proximate to the undersideor bottom of the larger diameter top portion 216 of the containmentvessel 200, and lower horizontal ends 220 b which terminate at orproximate to the base mat 304 of the concrete foundation 301. In oneembodiment, the external longitudinal fins 220 may have a height H3which is equal to or greater than one half of a total height of theshell of the containment vessel.

In one embodiment, the upper horizontal ends 220 a of the longitudinalfins 220 are free ends not permanently attached (e.g. welded) to thecontainment vessel 200 or other structure. At least part of the lowerhorizontal ends 220 b of the longitudinal fins 220 may abuttinglycontact and rest on a horizontal circumferential rib 222 welded to theexterior surface of the containment vessel shell 204 to help support theweight of the longitudinal fins 220 and minimize stresses on thelongitudinal rib-to-shell welds. Circumferential rib 222 is annular inshape and may extend a full 360 degrees completely around thecircumferential of the containment vessel shell 204. In one embodiment,the circumferential rib 222 is located to rest on the base mat 304 ofthe concrete foundation 301 which transfers the loads of thelongitudinal fins 220 to the foundation. The longitudinal fins 220 mayhave a lateral extent or width that projects outwards beyond the outerperipheral edge of the circumferential rib 222. Accordingly, in thisembodiment, only the inner portions of the lower horizontal end 220 b ofeach rib 220 contacts the circumferential rib 222. In other possibleembodiments, the circumferential rib 222 may extend (substantially)radially outwards far enough so that substantially the entire lowerhorizontal end 220 b of each longitudinal rib 220 rests on thecircumferential rib 222. The lower horizontal ends 220 b may be weldedto the circumferential rib 222 in some embodiments to further strengthenand stiffen the longitudinal fins 220.

The external longitudinal fins 220 may be made of steel (e.g. low carbonsteel), or other suitable metallic materials including alloys which areeach welded on one of the longitudinally-extending sides to the exteriorof the containment vessel shell 204. The opposinglongitudinally-extending side of each rib 220 lies proximate to, but ispreferably not permanently affixed to the interior of the inner shell310 of the containment enclosure structure (CES) 300 to maximize theheat transfer surface of the ribs acting as heat dissipation fins. Inone embodiment, the external longitudinal fins 220 extend(substantially) radially outwards beyond the larger diameter top portion216 of the containment vessel 200 as shown. In one representativeexample, without limitation, steel ribs 220 may have a thickness ofabout 1 inch. Other suitable thickness of ribs may be used asappropriate. Accordingly, in some embodiments, the ribs 220 have aradial width that is more than 10 times the thickness of the ribs.

In one embodiment, the longitudinal fins 220 are oriented at an obliqueangle A1 to containment vessel shell 204 as best shown in FIGS. 2-3 and5. This orientation forms a crumple zone extending 360 degrees aroundthe circumference of the containment vessel 200 to better resistprojectile impacts functioning in cooperation with the outer containmentenclosure structure (CES) 300. Accordingly, an impact causing inwarddeformation of the containment enclosure structure (CES) shells 210, 211will bend the longitudinal fins 220 which in the process will distributethe impact forces preferably without direct transfer to and rupturing ofthe inner containment vessel shell 204 as might possibly occur with ribsoriented 90 degrees to the containment vessel shell 204. In otherpossible embodiments, depending on the construction of the containmentenclosure structure (CES) 300 and other factors, a perpendiculararrangement of ribs 220 to the containment vessel shell 204 may beappropriate.

In one embodiment, referring to FIGS. 6-8, portions of the containmentvessel shell 204 having and protected by the external (substantially)radial fins 220 against projectile impacts may extend below grade toprovide protection against projectile strikes at or slightly below gradeon the containment enclosure structure (CES) 300. Accordingly, the basemat 304 formed at the top of the vertically extending sidewalls 303 ofthe foundation 301 where the fins 220 terminate at their lower ends maybe positioned a number of feet below grade to improve impact resistanceof the nuclear reactor containment system.

In one embodiment, the containment vessel 200 may optionally include aplurality of circumferentially spaced apart internal (substantially)radial fins 221 attached to the interior surface of the shell 204 (shownas dashed in FIGS. 2 and 3). Internal fins 221 extend (substantially)radially inwards from containment vessel shell 204 and longitudinally ina vertical direction of a suitable height. In one embodiment, theinternal (substantially) radial fins 221 may have a height substantiallycoextensive with the height of the water-filled annulus 313 and extendfrom the base mat 304 to approximately the top of the shell 204. In oneembodiment, without limitation, the internal fins 221 may be orientedsubstantially perpendicular (i.e. 90 degrees) to the containment vesselshell 204. Other suitable angles and oblique orientations may be used.The internal fins function to both increase the available heat transfersurface area and structurally reinforce the containment vessel shellagainst external impact (e.g. projectiles) or internal pressure increasewithin the containment vessel 200) in the event of a containmentpressurization event (e.g. LOCA or reactor scram). In one embodiment,without limitation, the internal fins 221 may be made of steel.

Referring to FIGS. 1-15, a plurality of vertical structural supportcolumns 331 may be attached to the exterior surface of the containmentvessel shell 204 to help support the diametrically larger top portion216 of containment vessel 200 which has peripheral sides that arecantilevered (substantially) radially outwards beyond the shell 204. Thesupport columns 331 are spaced circumferentially apart around theperimeter of containment vessel shell 204. In one embodiment, thesupport columns 331 may be formed of steel hollow structural members,for example without limitation C-shaped members in cross-section (i.e.structural channels), which are welded to the exterior surface ofcontainment vessel shell 204. The two parallel legs of the channels maybe vertically welded to the containment vessel shell 204 along theheight of each support column 331 using either continuous orintermittent welds such as stitch welds.

The support columns 331 extend vertically downwards from and may bewelded at their top ends to the bottom/underside of the larger diametertop portion 216 of containment vessel housing the polar crane. Thebottom ends of the support columns 331 rest on or are welded to thecircumferential rib 222 which engages the base mat 304 of the concretefoundation 301 near the buried portion of the containment. The columns331 help transfer part of the dead load or weight from the crane and thetop portion 216 of the containment vessel 300 down to the foundation. Inone embodiment, the hollow space inside the support columns may befilled with concrete (with or without rebar) to help stiffen and furthersupport the dead load or weight. In other possible embodiments, otherstructural steel shapes including filled or unfilled box beams, I-beams,tubular, angles, etc. may be used. The longitudinal fins 220 may extendfarther outwards in a (substantially) radial direction than the supportcolumns 331 which serve a structural role rather than a heat transferrole as the ribs 220. In certain embodiments, the ribs 220 have a(substantially) radial width that is at least twice the (substantially)radial width of support columns.

FIGS. 11-15 show various cross sections (both longitudinal andtransverse) of containment vessel 200 with equipment shown therein. Inone embodiment, the containment vessel 200 may be part of a smallmodular reactor (SMR) system such as SMR-160 by Htoltec International.The equipment may generally include a nuclear reactor vessel 500) with areactor core and circulating primary coolant disposed in a wet well 504,and a steam generator 502 fluidly coupled to the reactor and circulatinga secondary coolant which may form part of a Rankine power generationcycle. Other appurtenances and equipment may be provided to create acomplete steam generation system.

Referring primarily now to FIGS. 2-3, 16, and 18, the containment vessel200 may further include an auxiliary heat dissipation system 340including a plurality of internal longitudinal ducts 341circumferentially spaced around the circumference of containment vesselshell 204. Ducts 341 extend vertically parallel to the vertical axis VAand in one embodiment are attached to the interior surface of shell 204.The ducts 341 may be made of metal such as steel and are welded tointerior of the shell 204. In one possible configuration, withoutlimitation, the ducts 341 may be comprised of vertically orientedC-shaped structural channels (in cross section) positioned so that theparallel legs of the channels are each seam welded to the shell 204 fortheir entire height to define a sealed vertical flow conduit. Othersuitably shaped and configured ducts may be provided so long the fluidconveyed in the ducts contacts at least a portion of the interiorcontainment vessel shell 204 to transfer heat to the water-filledannulus 313.

Any suitable number and arrangement of ducts 341 may be provideddepending on the heat transfer surface area required for cooling thefluid flowing through the ducts. The ducts 341 may be uniformly ornon-uniformly spaced on the interior of the containment vessel shell204, and in some embodiments grouped clusters of ducts may becircumferentially distributed around the containment vessel. The ducts341 may have any suitable cross-sectional dimensions depending on theflow rate of fluid carried by the ducts and heat transferconsiderations.

The open upper and lower ends 341 a, 341 b of the ducts 341 are eachfluidly connected to a common upper inlet ring header 343 and loweroutlet ring header 344. The annular shaped ring headers 343, 344 arevertically spaced apart and positioned at suitable elevations on theinterior of the containment vessel 200 to maximize the transfer of heatbetween fluid flowing vertically inside ducts 341 and the shell 204 ofthe containment vessel in the active heat transfer zone defined byportions of the containment vessel having the external longitudinal fins220 in the primary annulus 313. To take advantage of the primarywater-filled annulus 313 for heat transfer, upper and lower ring headers343, 344 may each respectively be located on the interior of thecontainment vessel shell 204 adjacent and near to the top and bottom ofthe annulus.

In one embodiment, the ring headers 343, 344 may each be formed ofhalf-sections of steel pipe as shown which are welded directly to theinterior surface of containment vessel shell 204 in the manner shown. Inother embodiments, the ring headers 343, 344 may be formed of completesections of arcuately curved piping supported by and attached to theinterior of the shell 204 by any suitable means.

In one embodiment, the heat dissipation system 340 is fluidly connectedto a source of steam that may be generated from a water mass inside thecontainment vessel 200 to reject radioactive material decay heat. Thecontainment surface enclosed by the ducts 341 serves as the heattransfer surface to transmit the latent heat of the steam inside theducts to the shell 204 of the containment vessel 200 for cooling via theexternal longitudinal fins 220 and water filled annulus 313. Inoperation, steam enters the inlet ring header 343 and is distributed tothe open inlet ends of the ducts 341 penetrating the header. The steamenters the ducts 341 and flows downwards therein along the height of thecontainment vessel shell 204 interior and undergoes a phase change fromsteam to liquid. The condensed steam drains down by gravity in the ductsand is collected by the lower ring header 344 from which it is returnedback to the source of steam also preferably by gravity in oneembodiment. It should be noted that no pumps are involved or required inthe foregoing process.

According to another aspect of the present disclosure, a secondary orbackup passive air cooling system 400 is provided to initiate aircooling by natural convection of the containment vessel 200 if, for somereason, the water inventory in the primary annulus 313 were to bedepleted during a thermal reactor related event (e.g. LOCA or reactorscram). Referring to FIG. 8, the air cooling system 400 may be comprisedof a plurality of vertical inlet air conduits 401 spacedcircumferentially around the containment vessel 200 in the primaryannulus 313. Each air conduit 401 includes an inlet 402 which penetratesthe sidewalls 320 of the containment enclosure structure (CES) 300 andis open to the atmosphere outside to draw in ambient cooling air. Inlets402 are preferably positioned near the upper end of the containmentenclosure structure's sidewalls 320. The air conduits 401 extendvertically downwards inside the annulus 313 and terminate a shortdistance above the base mat 304 of the foundation (e.g. approximately 1foot) to allow air to escape from the open bottom ends of the conduits.

Using the air conduits 401, a natural convection cooling airflow pathwayis established in cooperation with the annulus 313. In the event thecooling water inventory in the primary annulus 313 is depleted byevaporation during a thermal event, air cooling automatically initiatesby natural convection as the air inside the annulus will continue to beheated by the containment vessel 200. The heated air rises in theprimary annulus 313, passes through the secondary annulus 330, entersthe head space 318, and exits the dome 316 of the containment enclosurestructure (CES) 300 through the vent 317 (see directional flow arrows,FIG. 8). The rising heated air creates a reduction in air pressuretowards the bottom of the primary annulus 313 sufficient to draw inoutside ambient downwards through the air conduits 401 thereby creatinga natural air circulation pattern which continues to cool the heatedcontainment vessel 200. Advantageously, this passive air cooling systemand circulation may continue for an indefinite period of time to coolthe containment vessel 200).

It should be noted that the primary annulus 313 acts as the ultimateheat sink for the heat generated inside the containment vessel 200. Thewater in this annular reservoir also acts to maintain the temperature ofall crane vertical support columns 331 (described earlier) atessentially the same temperature thus ensuring the levelness of thecrane rails (not shown) at all times which are mounted in the largerportion 216 of the containment vessel 200.

Operation of the reactor containment system 100 as a heat exchanger willnow be briefly described with initial reference to FIG. 19. This figureis a simplified diagrammatic representation of the reactor containmentsystem 100 without all of the appurtenances and structures describedherein for clarity in describing the active heat transfer and rejectionprocesses performed by the system.

In the event of a loss-of-coolant (LOCA) accident, the high energy fluidor liquid coolant (which may typically be water) spills into thecontainment environment formed by the containment vessel 200. The liquidflashes instantaneously into steam and the vapor mixes with the airinside the containment and migrates to the inside surface of thecontainment vessel 200 sidewalls or shell 204 (since the shell of thecontainment is cooler due the water in the annulus 313). The vapor thencondenses on the vertical shell walls by losing its latent heat to thecontainment structure metal which in turn rejects the heat to the waterin the annulus 313 through the longitudinal fins 220 and exposedportions of the shell 204 inside the annulus. The water in the annulus313 heats up and eventually evaporates forming a vapor which rises inthe annulus and leaves the containment enclosure structure (CES) 300through the secondary annulus 330, head space 318, and finally the vent317 to atmosphere.

As the water reservoir in annulus 313 is located outside the containmentvessel environment, in some embodiments the water inventory may beeasily replenished using external means if available to compensate forthe evaporative loss of water. However, if no replenishment water isprovided or available, then the height of the water column in theannulus 313 will begin to drop. As the water level in the annulus 313drops, the containment vessel 200 also starts to heat the air in theannulus above the water level, thereby rejecting a portion of the heatto the air which rises and is vented from the containment enclosurestructure (CES) 300 through vent 317 with the water vapor. When thewater level drops sufficiently such that the open bottom ends of the airconduits 401 (see, e.g. FIG. 8) become exposed above the water line,fresh outside ambient air will then be pulled in from the air conduits401 as described above to initiate a natural convection air circulationpattern that continues cooling the containment vessel 200.

In one embodiment, provisions (e.g. water inlet line) are providedthrough the containment enclosure structure (CES) 300 for waterreplenishment in the annulus 313 although this is not required to insureadequate heat dissipation. The mass of water inventory in this annularreservoir is sized such that the decay heat produced in the containmentvessel 200 has declined sufficiently such that the containment iscapable of rejecting all its heat through air cooling alone once thewater inventory is depleted. The containment vessel 200 preferably hassufficient heat rejection capability to limit the pressure andtemperature of the vapor mix inside the containment vessel (within itsdesign limits) by rejecting the thermal energy rapidly.

In the event of a station blackout, the reactor core is forced into a“scram” and the passive core cooling systems will reject the decay heatof the core in the form of steam directed upper inlet ring header 343 ofheat dissipation system 340 already described herein (see, e.g. FIGS. 16and 18). The steam then flowing downwards through the network ofinternal longitudinal ducts 341 comes in contact with the containmentvessel shell 204 interior surface enclosed within the heat dissipationducts and condenses by rejecting its latent heat to the containmentstructure metal, which in turn rejects the heat to the water in theannulus via heat transfer assistance provide by the longitudinal fins220. The water in the annular reservoir (primary annulus 313) heats upeventually evaporating. The containment vessel 200 rejects the heat tothe annulus by sensible heating and then by a combination of evaporationand air cooling, and then further eventually by natural convection aircooling only as described herein. As mentioned above, the reactorcontainment system 100 is designed and configured so that air coolingalone is sufficient to reject the decay heat once the effective waterinventory in annulus 313 is entirely depleted.

In both these foregoing scenarios, the heat rejection can continueindefinitely until alternate means are available to bring the plant backonline. Not only does the system operate indefinitely, but the operationis entirely passive without the use of any pumps or operatorintervention.

While the foregoing description and drawings represent some examplesystems, it will be understood that various additions, modifications andsubstitutions may be made therein without departing from the spirit andscope and range of equivalents of the accompanying claims. Inparticular, it will be clear to those skilled in the art that thepresent invention may be embodied in other forms, structures,arrangements, proportions, sizes, and with other elements, materials,and components, without departing from the spirit or essentialcharacteristics thereof. In addition, numerous variations in themethods/processes described herein may be made. One skilled in the artwill further appreciate that the invention may be used with manymodifications of structure, arrangement, proportions, sizes, materials,and components and otherwise, used in the practice of the invention,which are particularly adapted to specific environments and operativerequirements without departing from the principles of the presentinvention. The presently disclosed embodiments are therefore to beconsidered in all respects as illustrative and not restrictive, thescope of the invention being defined by the appended claims andequivalents thereof, and not limited to the foregoing description orembodiments. Rather, the appended claims should be construed broadly, toinclude other variants and embodiments of the invention, which may bemade by those skilled in the art without departing from the scope andrange of equivalents of the invention.

What is claimed is:
 1. A nuclear reactor containment system andcontainment protection system comprising: a containment vesselcomprising a cylindrical steel shell that surrounds a wet well, thecontainment vessel defining containment space configured for housing anuclear reactor containing a nuclear fuel core emitting heat, thereactor disposed in the wet well; a containment enclosure structuresurrounding the containment vessel and comprising a hollow cylindricalsteel shell; and a concrete foundation comprised of a bottom slabsupporting the cylindrical shell of the containment vessel andvertically extending sidewalls rising from the slab forming a top basemat supporting the containment enclosure structure, a lower portion ofthe containment vessel being positioned inside the sidewalls of theconcrete foundation below the base mat and an upper portion of thecontainment vessel extending upwards from the base mat; a water-filledannular reservoir formed between the containment vessel and containmentenclosure structure for serving as the heat sink for the heat generatedinside the containment space, the annular reservoir extendingcircumferentially around a perimeter of the upper portion of thecontainment vessel above the base mat and the lower portion ofcontainment vessel extending below the annular reservoir; wherein theannular reservoir is configured to cool the containment vessel byreceiving heat generated within the containment vessel.
 2. The system ofclaim 1, wherein the annular reservoir contains water for cooling thecontainment vessel.
 3. The system of claim 2, wherein the upper portionof the containment vessel above the base mat includes substantiallyradial heat transfer fins disposed in the annular reservoir andextending between the containment vessel and containment enclosurestructure.
 4. The system of claim 3, further comprising acircumferential rib attached to the containment vessel, the heattransfer fins having bottom ends coupled to the circumferential rib,wherein the circumferential rib is seated on the foundation.
 5. Thesystem of claim 2, wherein the containment vessel includes an internalsurface which contains extended surface area defined by a plurality ofradial fins to enhance capture of heat energy from the containmentspace.
 6. The system of claim 2, wherein the air cooling system isoperable to draw outside ambient air into the annular reservoir throughthe air conduits to cool the containment vessel by natural convection.7. The system of claim 2, wherein wetted portions of the annularreservoir are coated or lined with a corrosion resistant material. 8.The system of claim 1, wherein a portion of the water in the annulus isevaporated and vented to atmosphere through the containment enclosurestructure in the form of water vapor.
 9. The system of claim 1, furthercomprising an air cooling system including a plurality of vertical inletair conduits spaced circumferentially around the containment vessel inthe annular reservoir, the air conduits being in fluid communicationwith the annular reservoir and outside ambient air external to thecontainment enclosure structure.
 10. The system of claim 1, furthercomprising an upper annulus formed above the annular reservoir betweenthe containment vessel and containment enclosure structure, the upperannulus in fluid communication with the annular reservoir and a vent toatmosphere.
 11. The system of claim 10, further comprising head spaceformed between a top head of the containment vessel and a top of thecontainment enclosure structure, the head space forming a plenum influid communication with the vent to atmosphere and the upper annulus.12. The system of claim 1, wherein the containment vessel includes ashell having a diametrically enlarged top portion which overhangs lowersmaller diameter portions of the shell.
 13. The system of claim 12,further comprising a plurality of vertical support columnscircumferentially spaced around the perimeter of the containment vessel,the support columns engaging and operable to help support the topportion of the containment vessel.
 14. The system of claim 1, whereinthe containment enclosure structure has sidewalls comprised ofsubstantially radially spaced apart inner and outer concentric shellshaving concrete disposed in the annular space formed between the shells.15. The system of claim 1, wherein the containment enclosure structureincludes a top dome spaced vertically apart from a top head of thecontainment vessel.
 16. The system of claim 15, wherein the top head ofthe containment vessel is of radially symmetric curvilinear contour formaximum impact resistance.
 17. A nuclear reactor containment systemcomprising: a containment vessel comprising a cylindrical steel shellconfigured for housing a nuclear reactor containing a nuclear fuel coreemitting heat; a containment enclosure structure surrounding thecontainment vessel and comprising a hollow cylindrical steel shell; awater filled annulus formed between the containment vessel andcontainment enclosure structure for cooling the containment vessel; aplurality of substantially radial fins protruding outwards from thecontainment vessel and located in the water filled annulus; a concretefoundation comprised of a bottom slab supporting the cylindrical shellof the containment vessel and vertically extending sidewalls rising fromthe slab forming a top base mat supporting the containment enclosurestructure, a lower portion of the containment vessel being positionedinside the sidewalls of the concrete foundation below the base mat andan upper portion of the containment vessel extending upwards from thebase mat; the water filled annulus extending circumferentially around aperimeter of the upper portion of the containment vessel above the basemat and the lower portion of containment vessel extending below thewater filled annulus; wherein the water filled annulus is configured tocool the containment vessel by receiving heat generated within thecontainment vessel by the fuel core which is transferred to the waterfilled annulus via the substantially radial fins; wherein the water inthe annulus is heated and a portion is evaporated and vented toatmosphere through the containment enclosure structure in the form ofwater vapor.
 18. The system of claim 17, further comprising an aircooling system including a plurality of vertical inlet air conduitsspaced circumferentially around the containment vessel in the annulus,the air conduits being in fluid communication with the annular reservoirand outside ambient air external to the containment enclosure structure,wherein when a thermal energy release incident occurs inside thecontainment vessel and water in the annulus is substantially depleted byevaporation, the air cooling system being operable to draw outsideambient air into the annulus through the air conduits to cool thecontainment vessel by natural convection.
 19. A nuclear reactorcontainment system comprising: a containment vessel including acylindrical shell having an outer cylindrical wall, the cylindricalshell configured for housing a nuclear reactor containing a nuclear fuelcore emitting heat; a cylindrical containment enclosure structuresurrounding the containment vessel and comprising a hollow cylindricalsteel shell, the cylindrical containment having an inner cylindricalwall that faces the outer cylindrical wall; an annular reservoircontaining water and formed between the outer cylindrical wall and theinner cylindrical wall, the annular reservoir for cooling thecontainment vessel; a concrete foundation comprised of a bottom slabsupporting the cylindrical shell of the containment vessel andvertically extending sidewalls rising from the slab forming a top basemat supporting the containment enclosure structure, a lower portion ofthe containment vessel being positioned inside the sidewalls of theconcrete foundation below the base mat and an upper portion of thecontainment vessel extending upwards from the base mat; the annularreservoir extending circumferentially around a perimeter of the upperportion of the containment vessel above the top base mat and the lowerportion of containment vessel extending below the annular reservoir; aplurality of external substantially radial fins protruding outwards fromthe containment vessel into the annular reservoir and extending betweenouter cylindrical wall and the inner cylindrical wall; and an aircooling system including a plurality of vertical inlet air conduitsspaced circumferentially around the containment vessel in the annularreservoir, the air conduits being in fluid communication with theannular reservoir and outside ambient air external to the containmentenclosure structure; wherein the radial fins have bottom ends attachedto and supported by a circumferential annular rib attached to the outercylindrical wall of the containment vessel and protruding radiallyoutwards beyond the outer cylindrical wall, the circumferential annularrib seated on the top base mat of the foundation; wherein the annularreservoir is configured to cool the containment vessel by receiving heatgenerated within the containment vessel via the fins and transferringthe heat to the annular reservoir.